Services for older people with mental health problems are inadequate, an independent panel has warned.
Elderly people face discrimation in mental health services
More than 3.5 million older people have mental health problems according to the UK Inquiry into Mental Health and Well-Being in Later Life.
But years of under-funding and age discrimination in mental health services prevented people obtaining support and treatment, they said.
The government said they had set out guidance on improving services.
According to the inquiry, up to one in four people over 65 and two in five people over 85 - are suffering depression or serious symptoms of depression and one in five people over 80 suffers dementia.
There are also higher rates of suicide in people over the age of 75.
Yet older people with mental health problems are often ignored and receive little support, the Inquiry concluded.
It is estimated that two-thirds of older people with depression never even discuss it with their GPs, and of the third that do discuss it, only half are diagnosed and treated.
Even when they are diagnosed, older people are less likely to be offered treatment and the inquiry said some GPs believe depression is simply a symptom of growing older.
In 2006, a review of progress against the government's National Service Framework for Older People found that explicit age discrimination had not declined in mental health services.
And people over the age of 65 often receive different, lower cost and inferior services to younger people - even if they have same condition, the inquiry panel said.
Dr June Crown, chair of the inquiry, said mental health problems in later life were often preventable and treatable.
"Action to improve the lives of older people who experience mental health difficulties is long overdue.
"Current services for older people with mental health problems are inadequate in range, in quantity and in quality.
"Our report draws attention to groups of older people who are currently invisible in the UK, who have been denied the fair treatment that should be a hallmark of a civilised society."
Dr Crown told BBC Radio 4's Today programme rates of depression were increasing among older people.
She said: "What we are very concerned about is that older people don't get necessarily treatment for their depression even when they do report it to GPs.
"And if they do they're much less likely to be offered counselling and psychotherapy and are much more likely than younger people to be given tablets."
There needed to be much more coordination of policy and the government should give a minister responsibility for the issue, she added.
Gordon Lishman, director general of Age Concern who supported the inquiry said the years of ignorance, discrimination and underfunding must be overturned.
"The inquiry shows the true scale of the problems, but it also gives hope for the future in the shape of practical steps that can help the millions of older people suffering from a mental health problems."
Health Minister Ivan Lewis said: "This report raises fundamental questions for the NHS, care system, families and all communities as we face up to the challenge of an ageing society.
"Whether it be depression, chronic illness or dementia we have a duty to act so older people have the best possible quality of life.
"I will be taking the findings of this report seriously and working with stakeholders to seek continued improvements in the quality of mental health services for older people."
Chris Ball, chair of the Mental Health Network's older people sub-group, said: "It is vital that we tackle the issues of discrimination and stigma in mental health at all levels - both in the context of provision and in wider society."
Marjorie Wallace, chief Executive of the mental health charity Sane, said: "The standards of wards for elderly people with mental illness can be shocking, mixing patients with illnesses like depression and conditions like dementia.
"We entirely agree that age should not be a barrier to treatment for conditions such as depression and anxiety, which can be as successful with older people as with those in younger age groups."